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From: Nate Najar on 22 Nov 2005 01:43
So I've reconfigured my project studio to take advantage of more
inputs. I have a mackie onyx 1620 (traded in the 1220) and an maudio
1814. Previously I had been using a da78 as a converter into the
lightpipe in on the firewire interface. No problems- everythign sounds
great. Well I've added some keyboard type modules to my setup so I
need the line inputs on the mackie and i need to now use the analog
inputs on the firewire interface to accomodate these extra channels.
The mackie board has a balanced db25 connector for each set of 8
channels on the board. This db25 acts as a direct out, pre fader, pre
eq, etc.... I have a hosa snake running from the db25 out to the
analog ins on the fw. The fw ins are unbalanced. That's the
background. here's the problem:

I've discovered a terrible noise present at the analog ins of the fw
interface. it's almost like a white noise but with a high pitched beep
every so often. It prints to disk with pro tools, meaning it is AT the
input. I've checked every connection six ways from sunday, moved my
hardrive, etc etc etc, and I believe I've isolated the problem to the
db25 snake. The noise is not present at the channel inputs on the
mackie i am certain- I can solo the channels and turn up the gain with
no issue- but the db25 direct outs are delivering this noise. By
removing the db25 connector from the back of the board and leaving it
plugged in to the fw, the noise disappears. Unplugging the inputs from
the fw also gets rid of the noise.

My best guess is the unbalanced inputs are causing this. Any weight to
this theory? Is there a way to balance them? Would that solve my
problem? is there another way around the noise? As it exists it's
not something that can be ignored or tolerated. So as of now the
analog ins are useless. I can't run the modules directly into the fw
because I need everythign to run through the mackie for direct
monitoring purposes. It's also a patching/repatching issue. I hate
technology- I want a few mic pres and a tape machine and maybe I'll be
more productive AND make better recordings! This is getting
ridiculous.

Nate

From: Mike Rivers on 22 Nov 2005 07:42

Nate Najar wrote:
> So I've reconfigured my project studio to take advantage of more
> inputs. I have a mackie onyx 1620 (traded in the 1220) and an maudio
> 1814. I've added some keyboard type modules to my setup so I
> need the line inputs on the mackie and i need to now use the analog
> inputs on the firewire interface to accomodate these extra channels.

> The mackie board has a balanced db25 connector for each set of 8
> channels on the board. This db25 acts as a direct out, pre fader, pre
> eq, etc.... I have a hosa snake running from the db25 out to the
> analog ins on the fw. The fw ins are unbalanced.

That should be OK.

> I've discovered a terrible noise present at the analog ins of the fw
> interface. it's almost like a white noise but with a high pitched beep
> every so often.

> removing the db25 connector from the back of the board and leaving it
> plugged in to the fw, the noise disappears. Unplugging the inputs from
> the fw also gets rid of the noise.

That sounds like the noise is coming out of the Mackie when it's
connected to the computer through the Firewire interface. There's
probably something noisy that's getting on to the ground of the mixer
through a cable shield.

> My best guess is the unbalanced inputs are causing this. Any weight to
> this theory? Is there a way to balance them?

The unbalanced cables themselves aren't causing the problem, but it's
possible that if you had balanced inputs on the audio interface, you
might not have the problem. You could add transformers, but that would
be expensive.

Here are a few things to check that aren't too radical:

1. Connect the computer, the mixer, and the FW1814 (if it has an
external power supply) all to the same power strip. That will assure
that their grounds are all connected at a single point.

2. Is the computer connected to a network? If so, unplug the network
cable and see if the beeping goes away. The periodic beeping may be
caused by a "keep alive" data burst. On my Dell laptop, I had that
problem with the Mackie Firewire interface until I updated the network
card driver. Now the noise shows up every now and then, and reloading
the driver fixes it. Computers! Fooey!!!!

3. Disconnect all of the cables from the Onyx to the FW1814 but one and
see if you get the noise. See if it's coming in on all cables, some
cables, or just one cable. If you can get it with any cable, try
connecting just the ground - plug the cable into the jack so the sleeve
of the plug is touching the bushing of the jack, but no far enough in
so that the tip is making contact. This will tell you if the problem is
coming in through the cable shield or if it's actually coming out of
the Mackie.

4. Try a different output from the Mackie - connect an auxiliary send
or main output to the FW1814 input.

5. Do you have TV cable anywhere (electrically) near your audio system?
Is the computer connected to the living room stereo which is also
connected to the TV set or video recorder, which is connected to the
cable?

When you have a problem like this, you need to try a whole bunch of
things to try to isolate the source. You can't just fix it. Take data.
Pretend it's a lab project.

From: Scott Dorsey on 22 Nov 2005 09:46
Nate Najar <nate(a)natenajar.com> wrote:
>
>I've discovered a terrible noise present at the analog ins of the fw
>interface. it's almost like a white noise but with a high pitched beep
>every so often. It prints to disk with pro tools, meaning it is AT the
>input. I've checked every connection six ways from sunday, moved my
>hardrive, etc etc etc, and I believe I've isolated the problem to the
>db25 snake. The noise is not present at the channel inputs on the
>mackie i am certain- I can solo the channels and turn up the gain with
>no issue- but the db25 direct outs are delivering this noise. By
>removing the db25 connector from the back of the board and leaving it
>plugged in to the fw, the noise disappears. Unplugging the inputs from
>the fw also gets rid of the noise.

You have a ground loop. It's picking up RF trash from the computer.
>
>My best guess is the unbalanced inputs are causing this. Any weight to
>this theory? Is there a way to balance them? Would that solve my
>problem? is there another way around the noise? As it exists it's
>not something that can be ignored or tolerated. So as of now the
>analog ins are useless. I can't run the modules directly into the fw
>because I need everythign to run through the mackie for direct
>monitoring purposes. It's also a patching/repatching issue. I hate
>technology- I want a few mic pres and a tape machine and maybe I'll be
>more productive AND make better recordings! This is getting
>ridiculous.

Sit down and draw out where all your grounds go. You may need to take
your unbalanced signals into balanced inputs with the shields lifted.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
From: Nate Najar on 22 Nov 2005 12:12
thanks both of you.... I disconnected everyting in the rack
systematically (boy that took forever!) and i found it. It wasn't the
mackie like I thought. Well, not directly. My yamaha motif sound
module (that i bought 3 days ago) has a usb connection for a midi
interface. It's plugged into a usb hub. I unplugged the usb cable
from the yamaha and voila, instant silence. so now here's my problem-
how do you isolate such a connection so i can still use the usb midi
but not get all noisy?

Nate

From: Scott Dorsey on 22 Nov 2005 12:20
Nate Najar <nate(a)natenajar.com> wrote:
>thanks both of you.... I disconnected everyting in the rack
>systematically (boy that took forever!) and i found it. It wasn't the
>mackie like I thought. Well, not directly. My yamaha motif sound
>module (that i bought 3 days ago) has a usb connection for a midi
>interface. It's plugged into a usb hub. I unplugged the usb cable
>from the yamaha and voila, instant silence. so now here's my problem-
>how do you isolate such a connection so i can still use the usb midi
>but not get all noisy?

MIDI is supposed to be ground isolated. If it doesn't have isolation,
it doesn't meet the MIDI spec.

There are some optoisolator boxes out there that you can put in MIDI lines
to deal with this, because sadly a lot of gear out there doesn't meet
the MIDI spec either.

One of the first places manufacturers cut cost is in isolation... there
are also plenty of S-PDIF interfaces out there that have no transformers.
Of course, it winds up costing the customer more money in the long run
when they have to buy an isolation device....
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
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